The immune system is a very flexible one. This is mostly due to a large number of subsets of cells which co-exist and cooperate in the induction of the immune response. The study of these subsets is based largely on experiments using serological and functional markers to define these cells. Various functions of activated cells reflect differences in the composition of the surface membrane. Thus, the characteristics of the cell surface membrane are important factors in determining the physiological activity of that cell. There has been much speculation in recent years as to the role of glycosphingo-lipids (GSL) as functional constituents of the plasma membrane of mammalian cells, especially in transformed cells because of the many GSL changes which have been observed. There is however, little information on the exact physiological properties of individual GSL or on the role that they might play in transformation. We are proposing a research project which will contribute considerably to the basic understanding of the functional properties of GSL on the surface of normal and transformed cells. Recent developments in high performance liquid chromatography allow us to quantitatively analyze the GSL from as few as 5 x 10 to the 6th power cells. The use of monospecific antibodies to GSL in immunofluorescence studies permits the analysis of the distribution of GSL antigens on the surface of mouse lymphocyte subpopulations, and the fluorescence activated cell sorter allow us to separate these subsets. Functional experimental in vitro using well characterized techniques will allow us to correlate content, expression, and function of cell surface GSL in both normal and transformed mouse lymphocytes. We will then begin to understand the exact physiological activity of individual GSL at the molecular level.